1. Field of the Invention
This invention relates to continuous web-moving apparatus and in particular to thermally sensitive paper alignment and moving apparatus for printing thereon by a thermal printhead.
2. Description of the Prior Art
Continuous paper web-moving apparatus has been implemented with sprocket drives that involve levers, pawls and friction drives, all working in combination to keep the paper in alignment, generally for printing thereon. Such systems require relatively high cost and continuous adjustments.
Other systems use pinch roller techniques where the skew of paper is controlled by adjusting the pressure of the pinch on the paper at each each end of the driving pinch roller. In another system, the skew is adjusted by adjusting the pinch roller pressure at each end of the driven paper (This is the typical method of driving paper rolls in news print presses). In this latter prior art system, when the pinching pressure is light, the drive roller diameter must be large and the paper is then driven at a faster rate, moving toward the heavier pinching pressure.
This technique can be applied only to a limited degree with respect to a thermal line printer because of an out-of-round condition in the thermal printer caused by the force required between the printhead and the thermal paper to sufficiently heat the thermal paper. In the prior art system, the force applied across the printhead must be precisely uniform and the diameter of the print roll must remain substantially constant.
This invention reduces or eliminates these prior art disadvantages by maintaining the paper in tension between the supply roll and the drive roll to an extent that the paper is stiffened.